Spark-plug.



A. SCHMIDT.

SPARK PLUG.

APPLICATiON FILED JULY 29. ms.

Patented J une 19, 1917.

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UNITED STATES PATENT OFFICE.

ALBERT-scnivnbfr, or FLINT, Mien-lean, Assre von rocnhiii-ritonreinrronCOMPANY,

or FLINT, MICHIGAN, A conic-narrow OF MICHIGAN.

SPARK-PLUG.

Specification of Letters Patent.

Patented J line 19, 1917.

Application filed July '29, 1916. Sam ire/112,037.

b all whom it may concern:

Be it known that I, ALBERT SCHMIDT, a citizen of the RepublicofFrance,residing at Flint, in the county of Genesee and State of Michigan, haveinvented certain new and useful Improvements in Spark-Plugs, of whichthe following is a specification, reference being had therein to theaccompanying drawings.

The invention relates to spark plugs designed for use in connection withhigh-speed internal combustion engines, and it is the object of theinvention to obtain a construction which will withstand the hightemperature. There are two difliculties to be overcome in themanufacture of spark plugs for the use described; first, to maintain theinsulation so as to avoid short circuiting, and second, to dissipate theheat so as to avoid pre-ignition. here the heat is not too highelectrical insulation is best obtained by an extended insulator surfacebetween the elec trode and the casing. Inasmuch, however, as theinsulator is a comparatively poor conductor of heat this extendedsurface when used in high-speed engines often rises in temperature tothe pre-ignition point.

Again, where the insulator is exposed togreat differences of temperatureit frequently becomes cracked, resulting in short circuiting.

With the present invention, the insulator is ,so constructed andarranged as to provide for rapid dissipation of its heat and also toobtain a maximum length of insulating surface between the insulatedelectrode and the grounded electrode with the minimum amount of surfaceexposed to the heat. Provision is also made for avoiding unequal heatingof integral parts of the insulator so as to avoid fracture.

In the drawings:

Figure 1 is a longitudinal section through a spark plug embodying myinvention; and

Fig. 2 is a cross-section on line ww Fig. 1. I

A is the metallic casing provided with the usual threaded nipple B forengagement with the engine casing. C is an insulator arranged withinthis casing and forming a gastight joint therewith, preferably byfashioning the metal of the case while hot to bear against opposedshoulders E and D on the insulator Instead of extending the insulator Cso as to project beyond the casing A into the explosion chamber, it islimited in length to less than the case and a complementary insulator Fis arranged at its inner end. The latter is exposed to the heat ofexplosion, but as it is a separate member from the insulator Cfracturing, due to unequal heating, is avoided. The member F ispreferably in the form of a cylinder fitting within the casing A, itsinner surface being spaced from the electrode which extends axiallytherethrougln The inner end of the casing A is fashioned to bear againstthe inner end of the insulator F, and to form a gas-tight seal,preferably by the interposition of a gasket H, while the opposite end ofthe insulator is also provided with a gas-tight seal as described later.Thus the heat which is being imparted to the insulator is restricted tothe contact of the inner cylindrical surface with the combustion gases,while the larger outer surface is in heat-conductin g relation to themetallic casing A, and therefore provides a path for the dissipation ofheat. I

To assist in the dissipation of the heat, a metallic bearing ispreferably arranged at the end of the insulator sleeve F which isadjacent to the insulator C. which bearing is in heat-conductingrelation to the electrode I passing through the insulator C. As shown,this bearing J is formed of a memher which is separate from theelectrode I but is in contact therewith, and to this member J theextension electrode K is secured. This arrangement has the advantage ofpermitting independent movement of the inner insulator and electrode K.which lessens the danger of fracture. The oint between the bearing J andthe insulator F is gas-tight due to lapping. The gap between theinsulators is bridged by an insulator bushing L, preferably formed ofmica, which surrounds the inner end portion of the insulator C and alsolies between the insulator F and the casing A.

\Vith the construction as described, in use, the electrode K and theinner face of the insulator F are exposed to the high tempera ture ofthe combustion gases. The electrode is preferably formed of a materialwhich will stand this temperature, and the insulator by reason of itslarge heat-dissipating surface and relatively small surface exposed tothe heat, will be maintained at a temperature below the ignition.

What I claim as my invention is:

1. In a spark plug, the combination with the outer casing, of a two-partinsulator therein, the inner part being annular, means for forming agas-tight seal at opposite ends of? said. inner part, permittingmovement thereot in relation to said outer part, and an electrodeextending through the space within said inner part, having an electricalconnection extending outward through said outer part.

2. In a spark plug, the combination with an outer casing, of aninsulator therein formed in two parts, the outer part being fixed inposition relative to said casing-and the inner part being annular, anelectrode passing through the space within said an uular part and havingan enlargement extending between said inner and outer parts, means forforming a gas-tight seal at opposite ends of said annular part, and anelec trical connection through said electrode passing through said outerpart.

In a spark plug, the combination with an insulator formed in separateouter and inner parts, the inner part being annular, of a casingembracing and clamping the outer part and surrounding said inner part,the inner end 01": said casing overlapping the inner end of said annularpart, an electrode extending through the space in said annular part andhaving electrical connection passing through said outer part, and meansfor forming a gas-tight seal at opposite ends of said annular part.

i. In a spark plug, the combination of an insulator formed in separateouter and inner parts, the inner part being annular, a casing embracingand having a locking engagement with said outer part and surroundingsaid inner part, the inner end of said casing overlapping the inner endof said inner annular part, an electrode passing through the spacewithin said annular part and having an enlargement lying between saidpart and the outer part, means for forming a gas-tight seal at oppositeends of said annular part, and an insulator bridging the gap betweensaid inner and outer parts and lying between the same and said outercasing.

5. In a spark plug, the combination of an insulator formed in separateouter and inner parts, the inner part being annular, a casing embracingand fixedly secured to said outer part, surrounding said inner part, theinner end of said casing overlapping the inner end of said annularpart,an electrode extending through said annular part and having anenlargement lying between said inner and outer parts, means for forminga gas-tight seal at opposite ends of said annular part, and anelectrical conductor passing through said outer part in electricalcontact with but mechanically separate from said electrode to permitindependent movement of said inner and outer parts.

('3. In a spark plug, the combination With a casing, an insulatorindividually clamped therein and an electrode passing through saidinsulator, or an inner insulator member in the form of a hollow cylindersurrounded by said. outer casing and surrounding said electrode, andmeans for forming a gas-tight seal at opposite ends of said cylindricalinsulator.

7. In a spark plug, the combination with a casing having opposedshoulders, an insulator clamped between said shoulders and an electrodepassing through said insulator, of an inner insulator separate from saidfirst-mentioned insulator surrounded by said casing and surrounding saidelectrode, said inner insulator being movable relative to saidfirst-mentioned insulator. v

8. In a spark plug, the combination with an insulator, an electrodepassing through said insulator and a casing embracing and fixedlysecuring said insulator therein, oi an insulator separate from saidfirst-mentioned insulator surrounded by said casing and surrounding saidelectrode, said inner insulator being movable relative to saidlirstanentioned insulator and means upon said casing for retaining saidseparate insulator in position.

In testimony whereof I aflix my signature.

ALBERT SCHMIDT.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents. Washington, D. C.

